Photographic and printing media



Patented Dec. 26, 1939 UNITED STATES PHOTOGRAPIIIC AND PRINTING MEDIA Charles Dangelmajer, Niagara Falls, N. 12, as-

signor to E. I. du Pont de' Ncmours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application June 14, 1937, Serial No. 148,114

12 Claims. I

This invention relates to photographic and printing media. More particularly, it relates to improved light-sensitive compositions and to films, printing surfaces and the like formed therefrom, which are adapted to be used in a variety of photographic and printing processes.

The invention will be described with particular reference to photolithographic printing processes wherein the improved media of the invention possess exceptional utility.

The photolithographic processes now in general use involve printing from a photolithographic plate which comprises essentially a zinc or aluminum plate, on the surface of which the design portions have been rendered receptive to the printing ink while the other portions are nonink-receptive. In the direct printing process, the plate is usually mounted upon a roller which is revolved in contact with two other rollers. One

of the latter wets the hydrophilic portions of the plate with an aqueous "fountain solution; the other roller carries the oily printing ink and applies it to the hydrophobic surfaces of the plate which compose the design. The inked plate is then contacted with the paper or other material 0 to be printed. In the offset printing process, a

similar procedure is employed except that the design is first transferred from the lithographic plate to a rubber roller, thence from the latter no to the surface to be printed.

The photolithographic plates used heretofore have usually consisted of a zinc or aluminum plate coated with albumen or gelatine, with which is incorporated a light-sensitive agent, such as a dichromate, which is capable of causing hardening of the albumen or gelatine upon exposure to light. To produce the image upon such a plate, it is exposed to ultra-violet light under a photographic negative until photographic hardening of the exposed portions of the light-sensitive film is effected; the plate is then developed by washing with warm water, to remove the soluble portions of the film. Generally, a so-called developing ink is applied to the plate prior to the washing operation in order to insure that the insoluble portions, which define the image to be printed, will be receptive to the oily printing inks used.

Recently it has been proposed to replace the gelatine or albumen used heretofore as a basis 50 for light-sensitive layers with polyvinyl alcohol.

The latter materials has the advantage that itsproperties can be controlled more precisely than those of natural products like gelatine and albumen; also polyvinyl alcohol films possess great- 55 er mechanical strength and durability than those formed from gelatine or albumen. However, certain difficulties have been encountered in the practical utilization of polyvinyl alcohol films in photolithographic plates, one of the most im- 60 portant of which is the fact that they tend to lose their properties of ink receptivity after relativefy short periods of use. The loss of ink receptivity is especially pronounced when used polyvinyl alcohol plates are cleaned with solvents such as gasoline or turpentine. After such treat- 5 ment it is usually impossible to restore the ink receptivity of the polyvinyl alcohol film.

It is, accordingly, an object of the present invention to provide improved light-sensitive compositions adapted to be used for the production of printing surfaces and for general photographic purposes. It is a further object of the invention to provide printing media characterized by a high degree of ink-receptivity, durability and resistance to the action of water and 15 acids. Other objects will be apparent from the ensuing description of the invention.

The foregoing and related objects are accomplished by the incorporation in polyvinyl alcohol compositions utilized for preparing photographic 20 plates and other printing and photographic media of monobasic carboxylic acids containing 5 or more carbon atoms. We have found that films formed from such compositions possess an ink receptivity markedly superior to that of the usual polyvinyl alcohol films; that at the same time the new compositions have greater durability and resistance to an action of water, acids and. fountain solutions; and that, in general, the modifled polyvinyl alcohol compositions of the invention are superior to unmodified polyvinyl alcohol for practically all printing and photographic purposes.

In accordance with the invention, compositions suitable for preparing light-sensitive coatings on photolithographic and other printing surfaces and for the preparation of light-sensitive emulsions on photographic films and plates may be prepared by dissolving or dispersing a mono-basic carboxylic acid containing 5 or more carbon atoms, together with polyvinyl alcohol and a light-sensitizing agent, in water or other suitable solvent or dispersing medium. The resultant solutions or dispersions may be applied to a suitable support, for example, in the case of lithographic plates, to a zinc or aluminum plate, and the solvent removed by evaporation. The production of the image on the plate and its subsequent development and utilization in the printing process is effected in the same manner as with the gelatine or albumen media used heretofore.

Polyvinyl alcohol is a water-soluble, resin-like material which is usually obtained by the hydrolysis of polymerized vinyl esters, such as poly- 5 vinyl acetate. Polyvinyl alcohol can be made in a number of modifications of diiferent degrees of polymerization, the degree of polymerization depending largely upon the extent to which the polyvinyl compound from which it is derived has been polymerized. All of these modifications of polyvinyl alcohol are, to some extent, soluble in water. The more highly polymerized forms are less soluble and produce solutions of higher viscosities for equal concentrations than the lower polymers. There are also a number of the socalled partial derivatives of polyvinyl alcohol in which some of the hydroxyl groups in the molecule are replaced by other radicals, such as ester, ether or acetal radicals. Such partial derivatives may be produced by the incomplete saponification of vinyl esters or by the incomplete reaction of polyvinyl alcohol with acids, aldehydes or other compounds which react with hydroxyl groups. As would be expected, the properties of the partial derivatives of polyvinyl alcohol vary in accordance with the proportion of hydroxyl radicals that have been substituted for other' groups. When the hydroxyl radicals substantially predominate, the partial derivatives show essentially the properties of polyvinyl alcohol and, like pure polyvinyl alcohol, are soluble in water as distinguished from the esters, acetals, etc., which are soluble only in organic solvents. Accordingly, the term polyvinyl alcohol is used herein and in the appended claims to designate generically all of the foregoing modifications of polyvinyl alcohol including such partial derivatives thereof as contain a sufficient number of unsubstituted hydroxyl groups as to render the compounds soluble in water.

As the viscosity of a solution of polyvinyl alcohol of given concentration is a function of its degree of polymerization, I refer herein to the various polymers in terms of viscosity. It is to be understood that all such references designate the viscosity of a 4% aqueous solution of the polyvinyl alcohol at a temperature of 20 C.

A wide range of polyvinyl alcohol polymers are adapted for use in the compositions of the present invention. Thus, depending upon the particular purpose for which the compositions are toibe use], polyvinyl alcohol polymers having a viscosity of from about 2 to 60 centipoises may be used. In general, the lower polymers are more sensitive to slight difierences in light intensity, but are somewhat less resistant to water than the higher polymers. The higher polymers form somewhat more durable printing surfaces. In certain cases it has been found desirable to utilize mixtures of high polymers and low polymers.

The acids suitable for modifying the characteristis of polyvinyl alcohol in accordance with the invention include all monobasic carboxylic acids containing 5 or more carbon atoms. In the case of acids which are not normally water-soluble, it is advantageous to utilize them in the form of their water-soluble salts, e. g., as ammonium or alkali metal salts. It is not necessary, however, that-,the acids be dissolved in the composition, as satisfactory results may also be obtained by forming dispersions of the acids in the polyvinyl alcohol compositions. Moreover the acids may also be added in the form of their glycerides or other esters. Acids suitable: for modifying the polyvinyl alcohol compositions, in accordance with the invention, include: saturated aliphatic acids, such as valeric, caproic, enanthic, caprylic, pelargonic, capric, lauric, myristic, palmitic, stearic and behenic; unsaturated oliphatic acids, such as: undecylenic, oleic, elaidic, erucic, brassidic, eleostearic, linoleic, behenolic and ricinoleic; aromatic acids such as benzoic, naphthoic and toluic; alicyclic acids such as abietic, pimaric and naphthenic; and esters, such as olive oil,

cottonseed oil, linseed oil, China-wood oil, castor oil, methyl abietate, and butyl stearate. II desired, the corresponding acid anhydrides may be used instead of the acids.

The amount of higher acids utilized in the compositions may vary through rather wide limits, depending upon the purpose for which the composition is to be used and the result which it is desired to obtain. In general, the amount of acid may range from about 0.1% to 20% of the weight of the polyvinyl alcohol contained in the composition and will generally be within the limits of 0.3% to 5.0%.

The agents used to render the compositions light-sensitive may be any of those which have been used heretofore for similar purposes in gelatine or albumen films. For the preparation of photolithographic plates and for similar printing purposes, the preferred sensitizing agents are soluble chromium salts, such as, for example, ammonium dichromate or alkali metal dichromates. For the preparation of photographic emulsions, silver salts, especially silver halides, light-sensitive dyes and other sensitizing agents such as are well known in the photographic art may be employed.

The following examples are illusrative of certain specific embodiments of the invention:

Example 1 A composition was prepared from the following ingredients:

Parts by weight Polyvinyl alcohol (a polymer having a viscosity of 22 to 24 centipoises in 4% aqueous solution at 20 C.) 3.0 Ammonium dichromate 1.5 Ammonium linoleate 0.03 Water 95.5

- aqueous solution containing gum arabic with small amounts of phosphoric and gallic acids). The plate was then ready for use in the lithographic printing press.

The image on the plate thus prepared is uniformly receptive to the lithographic ink and retains such ink receptivity after long periods of use. The film possesses water-resistance superior to that of films made from unmodified polyvinyl alcohol. If desired, however, the water-resistance may be still further increased by heating the developed plate to a temperature of 80-120 C. for a period of 5 minutes to one-half hour.

Example 2 A composition was prepared using the same formula and procedure as gven in Example 1. with the exception that sodium oleate was used instead of ammonium linoleate.

Example 3 g A composition was prepared utilizing the same formula and procedure as in Example 1 except that ammonium ricinoleate was utilized instead of ammonium linoleate.

Example 4 A composition was prepared utilizing the same formula and procedure as in Example 1 except that potassium abietate was utilized instead of ammonium linoleate.

Example 5 Example 6 The procedure and formula of Example 1 was followed utilizing linseed oil in place of ammonium linoleate. The linseed oil was added to the polyvinyl alcohol solution in the form of a 10% aqueous emulsion, which was prepared by vigorously stirring 10 grams of linseed oil into 87 grams of water containing 3 grams of diglycol laurate as an emulsifying agent.

In certain instances the polyvinyl alcohol compositions of the invention can be combined with compositions used heretofore as a basis for lightsensitive films, such as albumen, gelatine, glue, gum 'arabic and the like. For special applications, dyes, pigments and filling agents of various kinds may be added to the compositions.

While the invention has been described primarily from the standpoint of the production of improved photolithographic plates, it is to be understood that the utility of the compositions of the invention is not restricted to photol ithography or similar processes. They may be used advantageously in substantially all printing and photographic arts wherein gelatine or albumen compositions have been used heretofore. They are suitable for both positive and negative printing processes, whether the films be utilized as ink-receptive printing surfaces or as etching masks. The compositions may be used advantageously for coating paper or fabrics to produce carbon tissues such as are commonly utilized in intaglio printing and in certain types of photographic finishing. Another application of the compositions is in the photographic production of mesh stencils of the type where a photosensitive material is utilized as a mask for the nondesign portions of the stencil. The compositions of the invention may also be utilized as emulsion coatings for photographic films and plates, both positive and negative.

Printing plates prepared from the compositions of the invention are characterized by improved qualities of ink receptivity and by the retention of such ink receptivity even after long continued use. They are also considerably more resistant both to water and to acids thanfilms prepared from unmodified polyvinyl alcohols and are characterized by greater durability and. superior printing qualities.

It is to understood that the invention isjnot restricted to any of the specific embodiments described hereinabove but includes all such variations, modifications and equivalents as fall within the scope of the appended claims.

I claim:

1. A light sensitive layer comprising polyvinyl alcohol, an agent adapted to promote photochemical hardening of said polyvinyl alcohol and 0.1% to 20% of a monobaslc carboxylic acid containing at least 5 carbon atoms.

2. A light sensitive layer comprising polyvinyl alcohol, 0.1% to 20% of a monobasic carboxylic acid having at least 5 carbon atoms and a water soluble chromic acid salt in light sensitizing amount.

3. A light sensitive layer comprising polyvinyl alcohol, 0.1% to 20% of a monobasic carboxylic acid having at least 5 carbon atoms and a water soluble dichromate in light sensitizing amount.

4. A light sensitive layer comprising polyvinyl alcohol, a water soluble salt of 0.1% to 20% of a monobasic carboxylic acid containing at least 5 carbon atoms and an agent adapted to promote photochemical hardening of said polyvinyl alcohol.

5. A composition comprising polyvinyl alcohol, 0.1% to 20% of a water soluble salt of linoleic acid and a light sensitizing agent.

6. A composition comprising polyvinyl alcohol, 0.1% to 20% of ammonium linoleate and ammonium dichromate in light sensitizing amount.

7 A printing device having on its printing surface ink receptive design portions, said ink receptive portions comprising photochemically hardened polyvinyl alcohol and 0.1% to 20% of a monobasic carboxylic acid containing at least 5 carbon atoms.

8. A printing device having on its printing surface ink receptive design portions, said ink receptive portions comprising photochemically hardened polyvinyl alcohol and 0.1% to 20% of a water soluble salt of linoleic acid.

9. A method of producing a photographic or printing device which comprises forming a film comprising polyvinyl alcohol, an agent adapted to promote photochemical hardening of said polyvinyl alcohol, and 0.1% to 20% of a mono basic carboxylicacid having at least five carbon atoms, and selectively exposing said film to light. 10. A method of producing a photographic or printing device which comprises forming a film comprising polyvinyl alcohol, an agent adapted to promote photochemical hardening of said polyvinyl alcohol, and 0.1% to 20% of a monobasic carboxylic acid containing at least five carbon atoms, selectively exposing said film to light and developing the exposed film to remove nonexposed portions thereof. 1

11. A method of producing a photographic or printing device which comprises forming a film comprising polyvinyl alcohol, an agent adapted to promote photochemical hardening of said polyvinyl alcohol, and 0.1% to 20% of a water soluble salt of linoleic acid, and selectively exposing said film to light.

12. A method of producing a photographic or printing device which comprises forming a film comprising polyvinyl alcohol, an agent adapted to promote photochemical hardening of said polyvinyl alcohol, and 0.1% to 20% of a water soluble salt of linoleic acid, selectively exposing said film to light and developing the exposed film to remove non-exposed portions thereof.

CHARLES DAN GELMAJEB. 

